1. Field of the Invention
The present invention relates to a device for measuring three dimensional shape.
2. Background Art
Generally, when electronic components are mounted on a printed board, firstly cream solder is printed at certain positions on the electrode pattern. Thereafter, the electronic components are temporarily fixed to the printed board by use of viscosity of the cream solder. Thereafter, the aforementioned printed board is conveyed to a reflow furnace, the printed board is subjected to a certain reflow step, and soldering is performed. In recent years, inspection of the printed state of the cream solder has been required at a stage prior the printed board being conveyed to the reflow furnace. A device for measuring three dimensional shape is used during this inspection.
In recent years, there have been proposals for various types of devices for measuring three dimensional shape by the use of light (so-called contact-free devices for measuring three dimensional shape), such as technology relating to devices for measuring three dimensional shape using the phase shift method.
A device for measuring three dimensional shape using this phase shift method uses an irradiation unit composed of a light source emitting a certain light and a grating for transformation of this light from the light source to a light pattern having a sinusoidal wave pattern (stripe-shaped pattern) to irradiate the light pattern on the object to be measured (i.e., a printed board in this case). Then, a point on the board is observed using an imaging unit disposed directly above the board. A charge-coupled device (“CCD”) camera or the like composed of a lens, an imaging element, or the like is used as the imaging unit. In this case, the intensity I of light at a point P on the image plane is given by the below listed formula:I=e+f×cos φ
(within the formula, e=non-modulated light noise (offset component), f=sine wave contrast (reflectivity), and φ=phase imparted by roughness of the object).
Here, due to movement or switching control of the aforementioned grating, the phase is changed, for example, in 4 stages as φ+0, φ+π/2, φ+π, and φ+3 π/2. Images of the corresponding intensity distributions (I0, I1, I2, and I3, respectively) are read, and the modulated component a is found based on the below listed formula.α=arctan {(I3−I1)/(I0−I2)}
Using this modulated component, the three dimensional coordinates (X, Y, Z) of the point P on the object to be measured, such as a cream solder or the like of a printed board, are found, and these coordinates are used to measure three dimensional shape (particularly height) of the object to be measured.
However, when using only a single aforementioned irradiation unit, shadowed parts may occur where the light pattern is not irradiated on the object to be measured (measurement subject). Thus, there is concern that accurate measurement of such shadowed parts may not be possible.
In consideration of such circumstances, technology is being proposed for the performance of measurement by irradiation of light patterns from two directions in order to improve measurement accuracy or the like.
Previously in this case, while a grating of a first irradiation unit has been shifted sequentially (or switched), an entire set of image data (e.g., 4 images of image data) has been imaged within a certain measurement subject range (image range) under illumination by a first light pattern having multiply shifted phases. Thereafter, while sequentially shifting or the like a grating of a second irradiation unit, an entire single set of image data is imaged within the aforementioned measurement subject range under illumination by a second light pattern having multiply shifted phases.
In contrast, in recent years, the second light pattern from the second irradiation unit is irradiated, and imaging is performed, while the grating of the first irradiation unit is being shifted or the like, and on the other hand, the first light pattern from the first irradiation unit is irradiated and, imaging is performed, while the grating of the second irradiation unit is being shifted or the like, so that irradiation and imaging are alternatingly repeated so that the measurement time can be shortened (for example, see the proposed technology of Patent Document 1).